For example, an on-demand inkjet head ejects ink drops toward recording paper, and an image is thereby formed on the recording paper. Such kind of inkjet head includes nozzles and actuators corresponding to each other one to one.
Piezoelectric actuators are formed on the surface of a substrate, and nozzle holes are formed corresponding to the actuators. Further, pressure cells are formed in the substrate corresponding to the actuators, the pressure cell starting from the back surface of the substrate and ending at the actuator. Further, ink is introduced from the back surface of the substrate and filled in the pressure cells, the actuators pressurize the ink filled in the pressure cells, and the inkjet head ejects the ink from the nozzle holes.
In the inkjet head, when printing, air bubbles may enter the pressure cells from the nozzles and the ink supply paths. In this case, the actuators cannot pressurize the ink, and the ink is ejected poorly. In order to recover from such poor ink ejection, it is necessary to stop printing, and to suck out the ink from the nozzles.